Polychrome beam light signal



Nov. 21, 1950 J, w, KNAPP 2,531,337

POLYCHROME BEAM LIGHT SIGNAL Filed Jan. 3, 1944 i 5 Sheets-Sheet 1Gttorneg J. W. KNAPP POLYCHROME BEAM LIGHT SIGNAL Nov. 21, 1950 FiledJan. 5, 1944 5 Sheets-Sheet 2 Nov. 21, 1950 J. w. KNAPP 2,531,337

POLYCHROME BEAM LIGHT SIGNAL w Gttomeg Nov. 21, 1950 J. w. KNAPPPOLYCHROME BEAM LIGHT SIGNAL 5 Sheets-Sheet, 4

Filed Jan. 3, 1944 ISnnentor Nov. 21, 1950 4, w, KNAPP 2,531,337

POLYCHROME BEAM LVIGHT SIGNAL Filed Jan. 3, 1944 6 Sheets-Sheet 5FIG.12.

,1126 114w 11a12 P +W 110 mi -l Snventor emitted light beam.

Patented Nov. 21, 1950 I POLYCHROME BEAM LIGHT SIGNAL James W. Knapp,Brockport, N. Y., assignor to General Railway Signal Company, Rochester,

Application January 3, 1944, Serial No. 516,815

' 4 Claims.

V This invention relates, in general, to light signals of thesearch-light type, and has more particular reference to a signalemitting a polychrome light beam and particularly adapted for theguidance of aircraft and water surface craft.

The signal, in accordance with the present invention, is somewhatsimilar to that disclosed in the S. P. Saint application, Ser. No.443,116, filed May 15, 1942 now Patent Number 2,4 5, AS in suchapplication, the signal is contemplated as being employed as a rotating,variably tilting type of signal for defining the approach to a landingfield, or as a tilted, non-rotatable signal for defining a glide pathfor aiding a plane to land on an'adjacent landing runway.

One object of the present invention is to provide a signal producing aglide light path limited on opposite sides, either ina vertical or ahorizontal plane, by light beams of distinctive characters.

Another object of the present invention is to provide means foraccurately controlling the angular spread of the beam constituting theglide path.

, cause the region in which they overlap to be of a distinctivecharacter of light.

Another object of the presentinvention is to provide means in the signalwhereby no light from g the light sourceemployed can pass directly tothe outside of the signal, and so that it must very largely first bereflected from a controlling reflector before emerging from the signal,whereby to very accurately control the character of the Another objectof provide means for readily adjusting the tilt of the signal withrespect to the horizontal, and for readily reproducing a predeterminedtilt, in the field, and after'repair to or replacement of parts in thesignal.

Further objects, purposes and characteristic features of the presentinvention will appear as the description progresses, reference beingmade to the accompanying drawings showing, solely by 2 Fig. 4 is afragmentary, elevational view of mounting and adjustin means for thesignal unit.

Fig. 5 is a wiring diagram of control circuits and devices for thesignal.

Fig. 6 is a diagrammatic side elevational view of the mounting andadjusting means for the signal unit.

Fig. '7 is a wholly diagrammatic view of a modified form of signal inaccordance with this invention.

Fig. 8 is a wholly diagrammatic view of a sec- I 0nd modified form ofthis signal.

the present invention is to the focal point of the reflector.

way of example, and in no way in a limiting sense,-

several forms which the invention can assume.

I In the drawings:

1 Fig.1 is a fragmentary sectional elevation of a I signal in"accordance with this invention with with parts shown in full.

Fig. 2 is a fragmentary, sectional plan view of I the signal with partsshown in full.

Fig. 3 is a wholly diagrammatic view of a por- 'tionof oneopticalsy'stem employed in this inv'ention.

Fig. 9 is a diagrammatic view of a portionof the form of signal of Fig.8.

Fig. 10 i a diagrammatic view of a portion of the form of signal of Fig.8.

Fig. 11 is a wholly diagrammatic view of a third modified form of theinvention.

Fig. 12 is a wholly diagrammatic View of any of the signals inaccordance with this invention, and of the beam as projected upon ascreen.

Fig. 13 is a wholly diagrammatic view of the application of any of thevarious forms of signals in accordance with this invention as applied tothe control of water surface craft.

Referring now to the drawings, and first to Figs. 1 and 2 thereof, thereis shown one form of a light signal in accordance with the presentinvention. The signal is of the general type as disclosed in the patentto E. W. Moore, No. 2,035,397, granted March 24, 1936, and accordingly,the details of the construction and adjustments need not be pointed outwith any great particularity as reference therefor can be made to thispatent.

The signal comprises a casing l5 having a front cover l6 hinged theretoas at I! and securable in place, when closed, by a threaded member R8.The casing has secured to it by suitable means, such as bolts 19, aparabolic reflector 20.

A light source in the form of an incandescent bulb 21 is employed, andthis bulb has a concentrated type filament 22 which is centered at Thelamp 2| is received in a socket 23, suitably secured to a bracket 24,one end of which is slidable in a holding member 25, while the other end25 is carried on a cam (not shown) forming part of an adjusting screw 21received in a threaded boss 28 of the casing and capable of beingclamped in adjusted position as by a nut 29. By means of the adjustingscrew 21 and its cam, the end 26 of the bracket can be moved in threedillerent directions at right angles to each other whereby 3 Thefilament is supplied with energy through lead-in wires 30 and 3! whichare received in a suitable openin 32 in the casing.

The front of the cover I6 carries an extending member i6 for receiving asun-shade or visor in the usual manner.

Cover i is supplied with an optical system including a front prismaticlens 33 having a plurality of vertical fluted portions or prisms as at34, for example, whereby to produce a desired horizontal spread in theemitted beam of an angle of perhaps to each side of the central axis.

To the rear of lens 33 is a lens 35 of the prismatic type and having aplurality of horizonally positioned flutes or prisms as at 36. Theseprisms are convexed outwardly, and where they join each other is a lowor root portion, and at the center line of each is a high, or crownportion.

To the, rear of'lens 35 is. positioned a plurality of color filtersextend p a e w the p There are two filters to each flute, one extendingfrom the crown to the root above as the filter 3i", and being a redfilter, and the other as 38,-

' arators when narrow enough, can be constituted by the film of cementbetween the filter edges.

It may, however, be here stated that the emitted light beam isconstituted by a green portion extending above the principal axis of.the lens system and a red portion extending below the principal axiswith an intermediate white or clear portion, at the axis, produced by anoverlap ofthe red and the green portions which red and green colors areso chosen as to combine and produce clear or white light.

The light from filament 22 very largely passes directly anduninterruptedly to the reflector from which it is reflected in paths atand substantially at right angles to the lens system to pass through thelenses and be emitted from the signal in the desired beam form. Toensure that light from the source shall not pass directly anduninterruptcdly to the lens system without having first been directed bythe reflector, a bafile in the form of a cylindrical opaque sleeve 39'is employed. This sleeve is fastened, in any suitable manner, to bracket24 and can be made of such opaque material as copper or the like. Sleeve39 is so proportioned and positioned, as shown in the drawing, thatlight from the filament cannot pass directly or uninterruptedly to thelens system without first at least having been reflected off variousopaque surfaces such as those o? the sleeve, the lamp base, etc. Hence,the

. only light which can materially contribute to the emitted beam islight which has been directed by the parabolic reflector.

The light signal, as described above, is mounted in an adjustable manneron. a supporting contrcl box M, which in turn is mounted on any suitablebase 42 (see Figs. 4 and 6). The top of the control box II is closed bya cover 43,,removably held in place, as by studs 44. The, top 43 isreinforced by ribs 45 to furnish suflicient strength to hold thesupported signal structure without danger of any bending or deformation.

The signal at its casing 16 is fastened as by bolts 43 passing throughholes 41 i the casing to a saddle-like curved member 48 formed as a partof a long angular beam structure 49, carrying adjusting bolts 50 and 5|received in the top. Beam 43 is pivoted as at 49 to rock on top 43 bymeans of sockets 52 in the beam received on studs 53 carried by top 43.By means of the adjusting bolts 56 and 5!, the beam, with its carriedsignal, can be tilted throughout any desired part of a given range andthen clamped tightly in place against the cover.

Carried by cover 43 is a line of sights constitilted by a fixed front,sight 55, and a movable rear, sight 56. The line of sight is afforded bysighting over the tops of these two sights. In the initial adjustment ofthe signal and during the final stages of manufacture, the signal ismounted as described just above on cover 43, and in front of it and atexactly 25 feet from the front of the signal box 4| is positioned ascreen, as 51, on which the beam from the signal is projected (see Fig.6). The top of box 4| is accurately leveled as by a spirit level. Thenthe light beam of the signal, projected on the screen, is adjusted inaccordance with accurate measurements by means of the adjusting bolts 50and 5|, to be accurately horizontal or level. The rear sight 58 is thenmoved on its adjusting stud 58 by means of a slot 59 in the sight toposition the line of sights so as to acciu'ately strike the center ofthe projection of the light beam on the screen. A mark on the casing top43, such as the mark 58 is made as a zero mark, directly opposite thezero graduation on the sight, and the sight is clamped in this position.

Thus, the sights are positioned to accurately determine a. horizontalbeam at a distance of 25 feet from the signal, and all that is necessaryfor positioning the signal to give a glide path of a specified angle isto position the rear sight with its angle designation opposite mark 58and adjust the signal lamp so that the center of the projected beam onthe screen at 25 feet is at the point Where the line of sights strikesthe screen.

With this arrangement of parts it is clear that with a portable screen,as 51, if it be necessary to replacev parts of the signal or repair thesame. the line of sights provided permits a ready subsequent adjustmentof the signal, so as to give the exact angle of glide path as thatpreviously given. For example, after a lamp has bee replaced, the screenis set up at 25 feet in front of the signal and after leveling, thesignal is adjusted by means of bolts 50 and 5| to position the center ofthe emitted beam accurately on the level where the line of sightsintersects. the screen. Thus, the desired angle of glide path is readilyobtainable in the. field even though a lamp be used for replacementwhich has a filament somewhat improperly positioned.

The wiring diagram of Fig. 5 shows the wiring and apparatus received incasing 41 for controlling the signal. The apparatus. for controlling thesignal and which is received in box 4| includes the above light bulb 2|,a toggle: switch 60, having central posts 6i and 62, which can, at will,be connected to upper posts 63 or lower posts 64, whereby to control thesignal by means of direct current from a Ill-volt; source as indicatedat 65, or by alternating current from a source as indicated at 66. Theapparatus includes in. ad-

dition arectifieril, a transformer 68 and a flashj""ing,relay,69. whichlatter can be of any suitable type as, for example, that disclosed inthe patfent to O. S. Field, No. 1,969,065, granted August Thefiashingrelay operates to make and break connection to the light source at anydesired rate, such as may be characteristic of the particular flocationwhere the signal is employed. With the toggle switch positioned foroperation by direct current, the direct current source supplies both thelight source and the flashing relay. j "the switch ispositioned tocontrol the signal by I alternating current, the transformer isconnected in circuit to provide for energizing the lamp with v theproper voltage of alternating current which When in the particular casein question is volts. The

alternating current is rectified by the rectifier and the rectifiedcurrent controls the flashing relayas is obvious from the showing inFig. 5.

. In this mannerthe signal, can be controlled "from either analternating or direct current source, and in each case the signal isflashed at any desired rate and preferably at a rate characteristic ofthe location of th signal.

Referring now to Fig. 3, there is here shown in a wholly diagrammaticfashion, a portion of the prismatic lens 35 of the signal shown in Figs.1

"and 2. This showing is not drawn to exact scale but is proportioned soas to more clearly show the principle of operation of the optical systemand still fit within the drawing space available.

' But a single complete flute or prism is shown together with portionsof the adjacent prisms.

There is here shown a complete prism it having a plane rear face, and aconvex front face. The curvature of the front face is so chosen as tocause the upper half thereof to refract light rays, striking the rearface at right angles thereto, to be deflected downwardly with respect tothe prin cipal axis H at an extreme angle of substantially The lowerhalf of the prism, in a similar manner, refracts such normal light raysup- 'wardly withrespect to the principal axis at an extreme angle ofapproximately 4. The angular I spread, it is of course to be understoodis vari-' able, in accordance with requirements, but as one specificexample, the above angle of 4 is chosen.

Above and below the prism 10 are shown portions 12 and 13 of adjacentprisms.

To the rear of the prismatic lens is a series of filters, the upper halfof each prism being backed up by a filter 14 to filter out all but thered light behind, While the lower half of each prism is a filter 15 tofilter out all but the green light,

the fragmentary portions of filters 16 and I! being inlike mannerrespectively green and red filters.

Between the separate filters ar opaque portions I8, 19 and 80 which arerelatively narrow and are 7 positioned to be accurately centereddirectly behind the places where the lens curvature changes critically,namely, at the roots and the crowns of the prismatic lens.

To the rear of the prismatic lens is shown a portion of the parabolicreflector 20 although as 1 stated above the relative positions of theparts is not shown accurately to scale, as space on the essarily has afinite size. Thus, three extreme the center 8| ofthe filament, which isplaced accurately on focus and the extreme sides 82 and 83, which arenecessarily'off focus all with respect'to the reflector, and hence thelight therefrom is affected differently by the prismatic lens. In thissignal it is of course apparent that light from every point of thefilament strikes every point on the reflector from which it is reflectedto pass through the filter and the prismatic lens to form the emerginglight beam.

Consider first the point 84 on the reflector which is on the principalaxis of the lens and consider light from the center 8| of the filamentstriking this point 84 as indicated by beam 85. This beam 85 leaves thereflector as beam 85a to strike the lens in -a normal direction and wereit not for the opaque portion 18 it would pass through the lens at thecrown and follow the principal axis II.

In the same manner light from the center of the filament indicated asbeam 85 and striking the reflector at point 81 leaves the reflector asbeam 81a to strike the lens ina normal direction at the root of the lensand emerge to form a beam as 81a in a direction parallel to theprincipal'axis of the lens were it not for the opaque portion 19. Thebeam 88a, originating at the center of the filament and striking thereflector at point 89, strikes the lens at the root of the lens and wereit not for the opaque portion 80 would emerge parallel to the principalaxis along line 88a.

Now consider point 90 on the reflector'which though greatly exaggeratedin the drawing is but very slightly inwardly of point 81. A beam 9|originating at the center of the filament and striking this point 90 ofthe reflector passes through the red filter 14 which it strikes in anormal direction leaves the reflector as beam 9m and is refracted by theupper half of the flute or prism 10 to be directed downwardly asindicated at am to limit the spread of the emerging beam to an angle ofsubstantially 4 below the principal axis. In a similar manner the point92 on the reflector which is but very slightly above point 89 reflectslight originating from the center of the filament and constituting abeam 93 as a beam 930. which passes through the green filter 15 which itstrikes in a normal direction and is refracted by the lower half ofprism 10 to be directed upwardly as the continuing beam 93a at an angleof substantially 4 above the principal axis whereby to thus limit thespread in an upward direction of the emerging signal beam.

Thus far, it is clear that these considered limiting beams define anemerging beam of a spread of substantially 8 measured in a verticalplane with the portion above the principal axis of a green color and aportion below the principal axis of a red color. Also, that each prismor flute of the entire prismatic lens will function in the same mannerto form a combined and continuous beam as viewed by an observer at ashort distance in front of a signal which will be of the same combinedcharacter as the character of the beam produced by each prism. This is,of course, due to the fact that at a short distance in front of thesignal the eye of an observer has not'sufficient resolving power to seethebeam from the separate prisms as separate beams. f

Considering now the points 94 and 95 on the reflector which althoughexaggerated ,in the drawing are but very slightly above and below theflection produces the beams 96b .and 960.

,is the only part that is accurately on focus has been considered. It isseen that with a true point source of light and a lens which isoptically pervfect, the resulting beam from the signal would comprise atWOrCOlOIGd ,beam with the upper half in this particular case of a'green color :and the lower-half of a red color.

Assumin for the moment what is almost invariably the case in practice,that the prismatic lens is .not optically perfect then at the roots andl at the crowns the outer surface of the lens for a very short distanceis flat and is parallel .to the .rear surface of the lens. In this case,:rays of light which strike the rear .-iace cf the lens norma'llywillpass through without being refracted and vso without crossing theoptical axis. Thus, the ray 96a, for example, instead .of passing belowthe axis would be above the axis and contribute red light to the portionof the :beam which the rear of the root portions of the :lens would passthrough the lens without refraction at these imperfect and substantiallflat portions of the lens, and would contribute to the beam .a colordifferent from what :is intended, and hence produce .a region where thecolors are mix-ed.

The net-result of all this is that with a true point source of lightwhich is, of :course, impractical if the lens [be slightly imperfectwhich in practice is very generally the case, a zone is produced in theemitted beam where thetwo colors are mixed and hence where a zone of adifferent :resulti-ng color is produced.

The green :and .red "filters referred to in this discussion are sochosen as to have the primary colors in such proportion that thecombination ;of the green and the red produces a white appearing beam.Thus, the emitted beam with such .an imperfect lens and such atheoretical point source of light i one that is green above and red.below with an intermediate zone of such a ture as to produce whiteappearing light to an observer having normal eyes.

Consider :nowthe light which .strikes the re- ,fractor and originates atthe sides 82 and 83 of the filament which filament in practice is :nec-

aessarily of .a finite size. It-can be seen that these mal and arepositioned either above or below the .normal. For example, at ,point 94ton the .reflector light from the edges of the ifilament on re- The:beam 96c is inclined to the normal .in the direc- ;tion that the lensretracts it and .hence passes across the principal axis and contributesred light to the contemplated red portion of the beam. With beam 9%,however, which is inclined in the opposite direction to the normal andhence opposite to the direction which the'lens refracts it, at the.crown of the lens, the curvature .of the lens even with .a lensoptically perfect will be insufficient to sufficiently retract it as tocause it to pass across the principal axis and hence this beam 961)produces an overlap of the colors above the principal axis.

In the case of point 84 on the reflector which is .on the optical axis,the light from the edges of the filament produces similar off-normalbeams 99b and 990 which in a manner similar to beam 96b are notsufficiently refracted by the lens even though the lens be perfect tocause them to cross the principal axis after having passed through theirfilters and the lens, and accordingly they produce an overlap of color.

It should be particularly noted that these beams reflected from theportion of the reflector that is on the principal axis produce a wideroverlap of color than does the light reflected from points above andbelow the principal axis. In other words, it is the light passingthrough the lens immediately adjacent the crown that produccs the widestoverlap and at points progressively removed from the crown the overlapproduced is progressively less in width until finally the curvature ofthe lens is sufiicient to sumciently refract the light to cause it topass across the principal axis and contribute its color to the part ofthe beam that is of the same color.

From the above it follows that by blanking .oil the light that wouldotherwise pass through the lens at the crown and immediately to eitherside thereof the overlap can be reduced in width as much as desired.Thus, the opaque portion 18 can be increased in width as desired todecrease as-desired the width of any overlap and this overlap is reducedfrom its outer edges inwardly toward the center.

Considering now and somewhat in detail the .optical system at the rootsof the lens, the light from the sides of the filament which strike thereflector at the point .90 produces beams 91b and 910 which strike thelens and filter inclined to the normal and respectively above and belowthe same. Beam Sic, which is sloped from the normal in the samedirection as the lens ,reiracts it, will close the principal axis andits red light will follow in the red portion of the emitted beam. Beam9112, however, which is sloped to the direction which the lens retractsit will still be .sufliciently reflected, unless the filament isunusually large, since the curvature of the lens at this point isrelatively sharp, so as to close the principal axis as indicated. If,however, the lens is imperfect, and relatively fiat at this point, thisbeam will proceed Without much, or any, refraction as the beam Slob andthus its red color will contribute to the beam above and below theprincipal axis, or in other words, will causean overlap. In order thatthe overlap can be properly controlled at the roots of the lens, in thecase of a relatively large filament, the opaque portions such as 19 and80, directly to the rear of the roots, are employed and can .be maderelatively narrow or wide to compensate for various imperfections and.sized filaments, such as occur in practice.

Considering the point 89 on the reflector, the light from the edges ofthe filament produce beams BBband 88c which are sloped to the normal andalso sloped in the direction which the lens white light,is of use inproducing a three-color beam with the overlapped portion showing aswhite light and forming a'glide'path for a landing plane, with the pathdefined above by the green portion of the beam and below by the redportion. In this manner a pilot following the white glide path isimmediately aware of the fact i when he has left the path and canascertain by the color of the beam he has entered, whether he i is aboveor below the proper path, and can accordingly control the plane .toimmediately bring him back in the white glide path. 7

InFig. 3 is indicated, in a wholly diagrammatic manner, the type of beamas it appears to an observer at a short distance in front of the signal.The red area extends asshown by line I03, from the lower edge of thebeam to well-above the principal. axis, and the green as shown by lineit extends from'theupper edge of the beam to well below the principalaxis, whereby-to produce a color overlap "as shown, by line I05. Inpractice this overlap with as perfect a lens as it is practicaltolobtain, and with as concentrated a filament as it is practical toemploy, is considerably too wide for practicaluse as a glide path.

In practice, with a-beam having a total angular spread of 8 ",,.'(4aboveand 4 below the principal axis) the overlapped portion is of theorder-of 2.

In practice, however," the overlap should not be more than about f. Inorder to properly limit this overlap angle and to cut it down from theouter margins inwardly, the'opaque portions as I8, 19 and 80 areemployed and are accurately positioned to the'rear of the lens anddirectly behind the critical crown and root lines and symmetricallypositioned to either side thereof. By

K increasing or decreasing these opaque portions,

the overlap can be reduced, or allowed to increase as desired. r

Asset forth"above,' the root portions of the lensare not as: critical asthe crown portions since there is an abrupt change in the curvature atthis point and even the off-normal rays due to the size of. the filamentcan be expected to be sufficiently refracted as to cross the principalaxis. If, however, the lens is not optically perfeet but has whatamounts to a flat portion at the root lines, then an overlap will beproduced unless thisportion of the lens is in efiect blanked ofi. by anopaque insert, such as I9. These inserts can be of any desired materialand in'one form are constituted. by a non-transparentjplasticfilledin'between the spaced ends of the filters.

At .the crown lines of. the. lens the curvature gradually changes fromone; direction through zero to the opposite direction and. at this zeropointpif thelens be opticallyimperfect, an over lap .will be formedeven; though the. filament be a truepoint source..

Furthermore, at these crown lines, even if the lens be opticallyperfect, the oft-normal rays due to the finitesize of the filamentstriking the lens slightly above and below the exact crown lines hence,anoverlap may result.

10 To briefly summarize the above, it can be seen that an overlap ofcolors is produced under various conditions, and is produced by thecrown portion and root portion of the prismatic lens. 3

Theoretically, the lens can be optically perfect and the light sourcecan be a true point source.

In practice, however, neither of these conditions can be exactlyfulfilled, and in many cases thelens is quite imperfect and has flatportions at' the root and the crown lines, while the filament has afinite size of considerable magnitude.

If the light source be a true point source and the lens be opticallyperfect, no overlap of colors I willoccur.

If the light source be finiteand the lens perf 'fectthen an overlap willoccur and is prodduced by the light beams at and adjacent to the crownsand adjacent to the roots.

crowns than at the roots wherethe curvature is reentrant. It is possiblethat thesize of the 1 filament may be such that an overlap is pro. ducedat the crowns but not at the roots. On' the other hand, the filamentmaybe of such an} extent, as compared to the curvatures involved that anoverlap is also .produced attherootsf When the lens is not-opticallyperfect, then the finite size filament produces a wider angle I ofoverlap, as is obvious from the discussion above,

By the. means described pose found desirable.

In but one practical embodiment of the invention, which has been founddesirable in practice, the filament employed is a small coil filament,about /64 inch in diameter, and about f /16 inch long, positionedhorizontally as shownfl; in the drawings. Ihe emitted beam is.one'having a spread in a vertical plane of 47 on each sideoftheprincipal' axis and with an overlap' central area having a totalangular spread of about &3" The opaque inserts such as 18 are. of awidth slightly less than thewidth of the filament, that is, about /32inch and the pris-g matic lens employed comprises 7 separate flutes}vpositioned horizontally with each flute about inch in height.

As explained above, lens 33 in front of the filter lensihas flutesrunning vertically and are designed to spread the light horizontallythrough an angle .of any desired amount and in one i specific case about5 to each side of the prin--" cipal axis was employed. 1 In the abovediscussion relating to Fig. 3 of the drawings it should be borne in'mind that points such as and 94 that are slightlyremoved from the lensroot and crown positions are shown on the drawings-to .an exaggeratedscale; in order to simplify the explanation. These relative positions isquite impractical, unless the scale of the drawing be increased many.iold.

Referring now to Fig. 12, there is here shown a light signal of aconstruction, as describ'ed above, having a casing 56 and emitting abeamasindicatediby dotted lines H0, which is; prof- .iected on"za. ,-screenv Ill positioned a: short dis This, as. explained above, is due to thefact that the di-. vergence of the edge rays is too great for the lenscurvature at these critical points to correct 1 by refraction. This ismore pronounced atthel' in detail above, a practical and simple means isprovided for pro- T ducing a three-color light beam of the correct f.angular spread and composition to-serve' in defining a landing glidepath or for any other pure T1 aortas-s7 tance, perhaps twenty-five feetfrom the signal. The projected beam then appears as illustrated andcomprises an upper relatively deep area IIZG, which is green in color, alike lower area II3'R, which is red in color and an intermediaterelatively shallow area IMW, which is the overlap and is white in color,and which comprises the desired glide path.

Referring now to Fig. 13, there is here shown how a' signal inaccordance with thisinvention can be usefully employed in the control ofwatercraft; A body of water H5 is shown and a chan nel therein is markedby two signals properly positioned, such as signals H6 and 1. Thesesignals are constructed in accordance with the above disclosure and arepositioned as shown to have a central white zone with a red zone to theleft and a green zone to the right, the signal having been rotated 90from the vertical in order to have the beam change in color in ahorizontal plane, rather than as before in a; vertical plane. Awatercraft entering the inlet I I8 can pick up the white path IIS andfollow it until the white path I23 is visible, whereupon it can followthis path I 28'. Ifthe craft should leave the white zone, and a greenzone is encountered it is clear the craft should bear to port, whereasif a red zone is encountered the craft should bear to starboard.

Other applications and use for this improved polychrome light signal mayreadily present themselves, and it is contemplated that all such.

uses should be covered by this application.

The light. signal as so far. described and as shown structurally,primarily in Figs. 1 and 2, employs a fluted or prismatic lens having aplurality of parallel prisms. This plurality of prisms is an advantageover a single prism in that an observer at a distance and viewing thesignal sees the entire circular lens as lighted by the colored light inwhich he stands, rather than seeing only a semi-circle of light if asingle .fiute should be employed. However, in the interest of iii Viewof the above and with reference to Fig.

'7, there is here shown a light signal of a modi'-. fied' form, theshowing being'wholly diagrammatic. It includes a casing I20, a lightsource f2! and a parabolic reflector I22. The lens employed comprises asingle flute I23 horizontally positioned and is provided with filters asdescribed above. The upper filter IE4 is a red filter and the lowerfilter I25 is a green filter. The resulting beam is substantially asdescribed above, and as indicated has a green portion, as shown by lineI26, a red portion as shown by line I21, these portions overlapping toproduce a white light glide path, as indicated by line I 28.

With regard to the form of invention shown in Fig; 7, the" opticalprinciples; and arrangements,

as described above, hold true, the only difference being that instead ofemploying" a plurality of 3 prisms in each signal, a single prism isemployed.

It may' be desirable to dispense with the separate' filters, asdescribed above, and employ lenses formed of colored transparentmaterial which function in the dual role of'lens" and filter.

Furthermore, in controlling the overlap, it may be desirable not toobscure or blank off portions of the lens asby means of opaque stepsback of the-liens, but to accomplish the same result by. removingthe-otherwise obscured portions of the,

lens. and bringingthe remainin'glens portionsfltd gether. Inother-words, at the'crown lines "the 12 curvature instead of graduallychanging ourvature has an abrupt change, while at the root por tions;the curvature changes from one to the other direction, at a slightlyshorter distance as measured from the crown point.

This form of the invention is, shown in Figs. 9 and 10. In Fig. 9 isshown one flute or prism in accordance with the above description, theupper portion I30 being formed of green transparent material such asglass to function as a lens and a green: filter, and. a lower portionf3'I being formed as a lens and a redfilter. Portions at the roots,indicated at I32 and I33 and the por tion' at the crown indicated atI34, which ortions in the forms earlier described would have beenblanked off by opaque strip portions are in this form removed entirely.Then the portions I38 and I 3| are brought together to form a completedflute, as shown in Fig. 10. This flute or prismthen operates, as isobvious, exactly" as does the constructionshown in Fig; 3, and describedabove in detail. However, in' many cases, this form or Fig. 10 may'beamuch simpler-and more economi cal form to producasineethe separatefilters have been eliminated, and the obscuring opaque" form. a signalemploying a polyfiiited prismatic lens, with the flutes, such as I35,formed a cescribed in connection with Fig. 10-, and having a lightsource I-36- andrefiector I31, whereby to produce a beam, as indicated,of a green color at Hill,

a red color at I39 and a white overlap as at I40.

It lets be understood that at times only the lens portions adjacent thecrown will be removed and the root portions not removed. Also, it iscontemplated that if desired the signal as" in Fig. 8 (and Fig. 11described below) can employ sepa" rate filters meeting at the center inwhich case the lensparts will be madeo: clear glass. K

In Fig. 11 is shown a further" modified form or the inventionwhichdiffers from the form shown in Fig. '7, only in that the single flute "2here employed is formed as shown in Fig. 10, and described above,namely, 50" as to eliminate the sepa-' rate filters and opaque portions.The beam pro duced is in accordance with what is described above inconnection with the various other forms, and as shown on the drawing,has a greenzorie I43, a red zone I, and. an overlap white zone I45.

In considering the above disclosure, it should. be constantly borne inmind that the drawings are in form and in manyca's'es without regard toaccurate. scale, in order" to bring out the various operative featuresand optical principles involved, without necessitating so Iarg'ea scaleas to be impractical on drawings somewhat limited as to size.

To briefly ummarize thefeatures described above in detail,- it maybeuseful" to briefly" rview various of the features. A signal fsproducedwhich (fail be til-ted, Witfi'in limits} at any desired angle to thehorizontal and which emits a beam having two distinctive colors,separated by a white portion, the white portion being obtained by aproper choice of the other; two colors" and by an overlaplofthesecolors. ue; to the necessarily 'finitlesizje-of' the filament whichmust" be employed in practice end/or the imperfect ons j in the Optical'chalractell'stics'idf the" lens'eswhi'cli' it practical to employ, theoverlap resulting 13 has too wide an angle of spread for practical use,and'henc'e means is provided for reducing the angular spread of thisoverlap to whatever extent it becomes desirable.

The above rather specific description of several forms and uses whichthis invention can assume has beenv given solely by way of example, andis not intended in any manner whatsoever in a limiting sense. Variousmodifications, substitutions and adaptations can be made as may fromtime to time appear practical or expedient without departing from thescope of the invention here disclosed and intended to be here protected,except insofar as it may be limited by the following claims.

Having described my invention, I now claim:

1. A light projecting signal for giving a polychrome beam for defining acourse comprising, a light projecting lens having a plurality ofparallel convex flutes each having a principal focus outside the signal,a light source of finite dimensions, a reflector for concentrating lightfrom said source to be projected by said lens into a narrow main beamalong the axis of the signal,

two filters of complementary colors for each flute 7 located in the pathof the light passing through that flute from said reflector, one of saidcolor filters determining th color of the light passing through oneportion of its flute to provide a narrow beam of one color on one sideof the optical axis of said flute, the other of said color filtersdetermining the color of the light passing through the other portion ofits flute to provide a narrow beam of light of the othercolor on the aother side of the optical axis of said flute, said reflector and flutescooperating with th finite dimensions of the light source to divert someof the light rays passing through the central portion of each of saidflutes away from its principal focus and provide a partial overlappingof the beams of different colors from such flute and its color filters,said overlapping portions of said different coored beams constituting adivergent beam of coalescing colors much narrower than the main beam ofthe signal and providing the visual efiect of a color distinctive fromeither of the colored beams alone, whereby the beam of overlapping andcoalescing complementary colors defines a narrow path along the axis ofthe signal having a visual aspect of color distinctive from thedifferent observable colors on the rechrome beam for defining a coursecomprising,

a lens system including a lens having a pluralty of parallel convexflutes and another lens for spreading the light beam in the planes ofsaid flutes, a light source of finite dimensions, a parabolic reflectorfor concentrating light from said source into substantially parallelrays along the axis of said lens system, a shield intercepting directrays from said light source through said lens system, two filters ofcomplementary colors for each flute, one of said filters determining thecolor of light passing through one-half of its flute to provide a narrowbeam of one color on one side of the optical axis of said flute, theother of said filters determining the color of the light passing throughthe other half of its flute to provide a narrow beam of light of theother color on the other side of the optical axis of said flute, saidreflector and lens system cooperating with the finite dimensions of thelight source to divert some of the light rays passing through the 1'4.central portion of each of said flutes and said color filters from itsprincipal focus and thereby provide a partial overlapping of the beamsof different co ors from such flute and its color filters,

-;said overlapping portion of said different colored beams constitutinga divergent beam along the axis of the main beam of the signal and muchnarrower in cross-section than said main beam,

the coalescing of the different complementary 1 colors in saidoverlapping portion having the visual effect of a color distinctive fromeither of the colored beams alone, whereby the main beam of said signalhas distinctive color aspects on opposite sides of a narrow beam of adifferent observable color to enable an observer to determine hisrelative position in said main beam of the signal.

3. A light projecting signal for giving a parabolic beam of threedistinctive colors for defining a course comprising, a source of lightof finite dimensions, a lens having a plurality of parallel convexflutes, a reflector for concentrating light from said source to beprojected by said lens into a relatively narrow main beam along the axisof the signal, a shield intercepting direct rays from said light sourcthrough said lens, a plurality of color filters located in the path ofthe light passing through said lens, each flute of said lens having twocolor filters of complementary colors for determining the color of thelight passing through different portions of said flute, each of saidflutes and its color filters cooperating with the flnite dimensions ofsaid light source to divert light rays passing through the centralportion of said flute from its principal focus and provide a partialoverlapping of beams of different colors from such flutes and its colorfilters, and a narrow opaque strip for each flute intercepting some ofthe light rays pass ng through said central portion of that flute tolimit the width of overlapping of said different colored beams, saidoverlapping portions of said different colored beams constituting adivergent beam of coalescing colors having a spread of less than twodegrees and providing the visual effect of a color distinctive fromeither of the colors of the colored beams, whereby the narrow divergentbeam of coalescent complementary colors along the axis of the main beamof the signal has a distinctive visual color aspect enabling an observerto determine his relative position in the main beam of the signal.

4. A light projecting signal for giving a polychrome beam for defining acourse comprising, a light source of finite dimensions, a parabo icreflector, a lens having a plurality of parallel abutting convex fluteswith root portions at their adjoining edges, a shield cutting offpassage of d rect light rays from said source through said lens, eachflute of said lens having two filters of complementary colorsdetermining the color of the light passing through opposit halves ofsaid flute, each of said flutes and its color filters cooperating withthe finite dimensions of said light source to divert rays of lightpassing through the central portion of said flute and the root portionsat its edges from the principal focus of said flute to provide a partialoverlapping of the different colored beams, said overlapping portions ofsaid different colored beams constituting a divergent beam of coalescingcolors having a distinctive color aspect from the color of either beam,and a plurality of narrow opaque strips located to intercept some of thelight passing through said central and root por- 15 tibns of said flutesto limit the spread of the beam of coalescing colors to less than twodegree's.

- JAMES W. KNAPP.

REFERENCES CITED UNITED STATES PATENTS Number Name Date 867,256 DioanOct. 1, 1907 1,230,669 Cassady et a1 June 19, 1917 1,266,554 Coleman eta1. May 21, 1918 1,348,855 Fass'enden Aug. 10, 1920 15 1,402,816 Wallis1- Jan. 10, 1922 1,429,067 Dole Sept. 12, 1922 1,432,659 Bochet Oct. 17,1922 Number Number Name Date Craig Jan. 16, 1923 Luby Dec. 18, 1923Howard Jan. 29, 1935 Spring Dec. 10, 1935 House May 5, 1936 ChalfantAug. 18, 1936 Scott et a1. Mar. 24, 1942 Farrand et a1 1- June 16, 19 12Roper Oct. 9, 1945 Flett 18, 1948 FOREIGN PATENTS Country Date GreatBritain of 1897 Great Britain May 1, 1924 France Mar. 11, 1922

